75. Sort Colors

    func sortColors(_ nums: inout [Int]) {
        if nums.count <= 1 {return}
        var n = nums.count

        var p0 = 0
        while p0 < n && nums[p0] == 0{
            p0 += 1
        }
        var p2 = n - 1
        while p2 >= 0 && nums[p2] == 2{
            p2 -= 1
        }

        var runner = p0
        while runner < n && runner <= p2{
            if nums[runner] == 0{
                nums.swapAt(runner, p0)
                runner += 1
                p0 += 1
            }else if nums[runner] == 2{
                nums.swapAt(runner, p2)
                p2 -= 1
            }else{
                runner += 1
            }
        }
    }